Periodic electrode structure for vacuum gap devices



J A- RICH Oct. 7, 1969 PERIODIC ELECTRODE STRUCTURE FOR VACUUM GAPDEVICES Filed May 19, 1967 3 Sheets-Sheet 1.

/nvem0r Joseph A. Ric/7,

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J. A. RICH Ucku 7, 1969 PERIODIC ELECTRODE STRUCTURE FOR VACUUM GAPDEVICES Filed May 19, 1967 3 Sheets-Sheet 2 &

50 i F/gA /nvenfor Joseph A. Ric/7 by QQ XL His Afro/nay.

J. A. RICH PERIODIC ELECTRODE STRUCTURE FOR VACUUM GAP DEVICES Filed May19, l '7 3 Sheets-Sheet 5 Joseph A. Ric/2 v His Afforney- United StatesPatent 3,471,734 PERIODIC ELECTRODE STRUCTURE FOR VACUUM GAP DEVICESJoseph A. Rich, Schenectady, N.Y., assignor to General Electric Company,a corporation of New York Filed May 19, 1967, Ser. No. 639,843 Int. Cl.1101i 17/04, 61/06 US. Cl. 313-217 8 Claims ABSTRACT OF THE DISCLOSURE JXB on the current paths between any adjacent opposite electrode pair issubstantially zero and bunching of current paths to form destructiveanode spots is avoided. Device may carry very high currents with verylow current density at any given point.

Related applications The present application is related to my copendingconcurrently filed applications, Ser. Nos. 639,693 and 639,- 834, andthe concurrently filed copending application of James M. Latferty, Ser.No. 639,844.

The present invention relates to vacuum gap devices adapted to operateat high current without the formation of anode spots therein. Moreparticularly, the present invention relates to such devices in which theformation of anode spots is avoided by the configuration and position ofthe electrodes such that essentially no magnetic field exists within theinterelectrode gap. Specifically, a pair of primary arc-electrodescomprising a plurality of electrode members are generally assembled sothat the individual electrode members interleave with one another toform a periodic structure which renders magnetic fields normal to theconduction paths within the interelectrode gaps vanishingly small toprevent the formation of anode spots.

In the development of vacuum switches and triggerable vacuum gapdevices, a limiting factor to the amount of current which can be drawnby a given structure is the threshold current at which a destructiveanode spot is formed. Formation of such anode spots results in erosionof the anode electrodes and melting thereof. Such erosion and meltingadversely effect the surface of the device, making the breakdown voltagechange from its original value, eventually leading to the failure of thedevice. This is because erosion of the electrodes leaves irregularsurfaces, which irregular surfaces cause perturbations in the electricfield, which facilitate the breakdown at lower voltages. In developingprior art vaccum gap devices, many attempts have been utilized in orderto keep anode spots from causing such destructive erosion. Generally,these attempts have been along the lines of accepting the fact thatanode spots are inevitable and constructing the electrodes of such aconfiguration and providing the interaction space with magnetic fields,either due to the action of the arc itself, or due to externalinfluences, so that the interaction of the magnetic field with theelectric arc causes the arc to move, generally by rotating around theperiphery of disc-shaped electrodes. Although these techniques areuseful and do in fact result in longer life than vacuum gap devices inwhich such attempts have Patented Oct. 7, 1969 not been made, much isleft to be desired in order to prevent the formation of anode spots.

In my copending application, mentioned hereinbefore, I have set forth mydiscovery leading to a new approach in the attack on anode spots invacuum gap devices. Briefly stated, I have found that it is notnecessary to accept the fact that anode spots must be lived with.Rather, since the body force or force per unit volume of conductingfluid acting upon any conduction path between a pair of arc-electrodesin a vacuum gap device is governed by the formula where F is body force,B is the magnetic field existing in the interelectrode gap, and J is thecurrent density between these elctrodes, in accord with the generaldiscovery set forth in the copending application, I eliminate orminimize the body force by eliminating or minimizing the normal magneticforce in the interelectrode gap. In one embodiment of the invention setforth in my copending application, I form an inner electrode from are-entrant cylinder wherein the current path is folded-back upon itself,and form the other electrode from a concentric cylinder surrounding thefirst electrode. Current flow in the outer cylinder is longitudinal andthus, by Amperes law, current flow within the exterior cylinder resultsin no net magnetic field within the confines of the cylinder. In theinner-electrode, current in one direction within the re-entrantstructure is substantially equal to current in the opposite direction inthe other section thereof and, hence, the net magnetic field isessentially zero exterior of the re-entrant inner-electrode.Accordingly, the interelectrode gap, which is a cylindrical annulusbetween the two concentric cylindrical electrodes, is essentiallymagnetic field-free and essentially no body force acts upon the currentpaths between the concentric electrodes. The current paths are,therefore, not caused to bunch-up at one end of the device, thus causingthe formation of destructive anode spots.

Although the class of devices described hereinbefore is a great advanceupon the prior art and essentially opens a new field of development forvacuum gap devices, I have found that the precise geometry necessary toobtain a magnetic field-free region in the interelectrode space isdiflicult to achieve. Similarly, if and when the device does fail, theentire active portion must be replaced. It is desirable that replaceableelectrode elements be incorporated therein in order to serve as a devicewithout completely replacing the electrode structure.

Accordingly, it is an object of the present invention to provide vacuumare devices wherein the electrode configuration greatly increases thecurrent threshold for the formation of anode spots without requiringclose tolerances and difficult configurations.

Yet another object of the present invention is to provide vacuum arcdischarge devices which are capable of carrying very high currentswithout the formation of anode spots and utilizing replaceable electrodemembers in the event of failure.

Still another object of the present invention is to provide vacuum arcdevices in which the interelectrode gaps are substantially free ofmagnetic fields which tend to cause bunching of the electric paths andthe consequent formation of anode spots in a configuration that issimple, economical to manufacture and easily maintained.

In accord with one embodiment of the present invention, I provideimproved vacuum arc discharge devices having high current thresholds forthe formation of anode spots and including a pair of primaryarc-electrode assemblies, each of which includes a plurality ofelectrode members and which are assembled together with the individualelectrode members interleaved or interdigitated together so as toprovide a plurality of interelectrode gaps, each of which issubstantially free from magnetic fields transverse to the path ofcurrent conduction between the individual electrode members. Such astructure facilitates the carrying of high currents between adjacentopposite poled electrode members due to the large electrode area withoutbunching thereof, with the resultant formation of destructive anodespots. In one embodiment of the present invention, conduction betweenopposite poled electrode members is initiated by the injection of anelectron-ion plasma into the interelectrode gap by the pulsing of thetrigger electrode assembly. In accord with another embodiment of thepresent invention electron-ion plasma is created within theinterelectrode gaps by the opening of a starter electrode which strikesan initial arc filling the device with plasma.

The novel features believed characteristic of the present invention areset forth in the appended claims. The invention itself, however,together with further objects and advantages thereof, may best beunderstood with reference to the following description, taken inconnection with the appended drawing, in which:

FIGURE 1 is a vertical cross-sectional view of a triggerable vacuum gapdevice constructed in accord with the present invention,

FIGURE 2 is a vertical cross-sectional view, with parts broken away, ofa vacuum switch constructed in accord with another embodiment of thepresent invention,

FIGURE 3 is a horizontal section view taken along lines 3-3 in FIGURE 1,

FIGURE 4 is a vertical cross-sectional view, with parts broken away, ofan alternative embodiment of the trigger vacuum gap device of FIGURE 1,

FIGURE 5 is a horizontal plan view in section illustrating analternative configuration to that illustrated in FIGURE 3,

FIGURE 6 is a schematic diagram illustrating the field configuration inthe vicinity of four electrode members of the device of FIGURE 4,

FIGURE 7 is a schematic illustration of current conduction paths betweenadjacent electrode members of the devices of FIGURES 1 and 4,respectively,

FIGURE 8 is a vertical cross-sectional view, with parts broken away, ofa triggerable vacuum gap device constructed in accord with anotherembodiment of the present invention,

FIGURE 9 is a horizontal sectional view taken along lines 9-9 of FIGURE8,

FIGURES 10 and 11 are horizontal section views of alternative structuresto that illustrated in FIGURE 9.

In vacuum are devices, the current threshold marking the onset of theformation of anode spots is a function of electrode geometry andelectrode material. For a given material, therefore, the formation ofanode spots is a function of electrode geometry. In the plane-parallelgeometry, frequently utilized in switches in general and vacuum switchesin particular, the threshold is relatively low, since a spot is formedat any point at which the current density becomes high, either due tosurface irregularities or anchoring of the are due to the interaction ofelectric currents and magnetic fields. One means of inhibiting theformation of anode spots is to use electrodes having a very large areaso that the current paths between the arc-electrodes are diffused over avery large area to lower the current density and prevent the formationof anode spots. Yet another means utilized to avoid the formation ofanode spots, or to facilitate the carrying of high currents withoutdestructive action of anode spots, is to utilize electrode configurationand magnetic fields, either caused by the current conduction paths or anexternal magnetic field, to interact to cause the arc to move over theelectrode surface, most generally to rotate about the P p y Of adisc-Shaped electro e,- his tends to keep the burning and erosion at anygiven point of the anode to a minimum.

In accord with the invention set forth in my copending application,realizing that the force tending to cause conduction paths between apair of oppositely-poled arcelectrodes to bunch together and form a highcurrent density which results in the formation of an anode spot to bethe result of the vector product of the current and the normal componentof the magnetic field, I eliminate or reduce the normal magnetic fieldso as to reduce the magnitude of the vector production and, hence, thebody force acting to propel the current conduction paths together, or tobunch or concentrate the arc discharge into a small region of thedischarge volume. In accord with the configuration disclosed in mycopending application, concentric cylindrical conductors are utilizedwith the inner conductor being re-entrant in structure to cause afoldingback of current therein with a net zero contribution to theazimuthal magnetic field in the interelectrode gap. In accord with thepresent invention, I find that it is not necessary to utilize aconcentric configuration for the primary arc-electrodes, but that,rather, a number of electrode members may be arranged in interleavedrelationship to form a periodic electrode structure in which magneticfields transverse to the current conduction paths are minimized oreliminated. Such structures give greater freedom for the construction ofvacuum are devices and facilitate the dissembly of a device that hasfailed to remove one or more electrode members without having to discardthe entire device.

FIGURE 1 illustrates a triggered vacuum gap device constructed in accordwith the present invention. In FIG- URE 1, triggerable vacuum gap 10includes an upper electrode assembly 11 and a lower electrode assembly12 joined with a cylindrical sidewall member 13 which is hermeticallysealed to lower electrode member 12 by a dielectric or insulating seal14. Upper electrode assembly 11 includes a base plate or disc 15 and aplurality of downwardly depending electrode members 16. Lower electrodeassembly 12 includes a plurality of upwardly depending electrode members18 and a base plate or disc 17. Each of the individual, downwardlydepending electrode members 16 includes a central post 19 and aconcentric cylindrical member 20 which is connected to central post 19at the inward end thereof by disc member 21. Similarly, each of theupwardly-depending electrode members 18 includes a central post 22 and aconcentric cylindrical mber 23 which is joined to central post 22 at theinner end thereof by disc member 24. The periodic structure caused bythe interleaving of downwardly-depending electrode members 16 andupwardly-depending electrode members 18 causes the creation of aplurality of interelectrode gaps 25. The active surfaces of thearc-electrode members include the cylindrical members 20 and 23 ofelectrode members 16 and 18 respectively and the end caps 21 and 24.These materials are prepared from a high purity, high vapor pressurematerial as for example, copper or any of the materials set forth inPatent 2,975,- 256, to Lee et al., Patents Nos. 2,975,255 and 3,016,436to Laiferty, and Patent No. 3,140,373 to Horn, and similar materials,alloys and intermetallic compounds which are operative to provide acopious quantity of metallic particles during arcing for the supplyingof conduction carriers during operation of the device.

During operation, it is essential that none of the aforementionedvaporized metallic particles be deposited upon the iusulator separatingthe opposite electrode assemblies. Accordingly, ceramic or otherinsulating seal member 14 is protected by the bafiling arrangementprovided by the lower end of sidewall member 13 and an annular flange 26projecting upwardly from base member 17 of electrode assembly 12. Inoperation, a high voltage is connected between terminals 30 and 31electrically in contact with electrode assemblies 11 and 12,respectively, and in circuit with an electric load tov be protected,

switched, or otherwise controlled. When it is desired to cause thedevice to change from a non-conducting to a conducting state, a pulse ofelectron-ion plasma is injected into the volume within device 10 fromtrigger assembly 27. Trigger assembly 27 includes a trigger anode 28 anda trigger cathode 29 in electrical contact with arcelectrode assembly12. Trigger electrode 28 may conveniently comprise a metallized ceramiccylinder with a scored gap therein with the metal on one side of the gapconnected electrically to trigger cathode 29 and the metal on the otherside of the gap connected to a trigger anode lead 32. Although asimplified trigger assembly is shown herein, it is to be understood thatany suitable trigger assembly operative to inject a cloud of electronionplasma into the interaction space between the arcelectrode members issuitable. Some such triggers are illustrated, for example, in thecopending applications, Ser. Nos. 516,941; 516,942; and 516,943, of J.M. Lafferty, filed Dec. 28, 1965.

In operation, when a pulse of electron-ion plasma is injected into theinteraction space, the plurality of interelectrode gaps 25 betweenindividual electrode members 16 and 18 become the site of a number ofsmall arcs or conduction paths with the conduction paths spreadingrapidly over the many broad areas presented by the closest surfaces ofthe individual electrode members. The conduction paths are limited tothe interelectrode gaps 25 because these are the shortest distancesbetween any points in the device 10 which are electrically at thepotential of the primary arc-electrodes. Although FIGURE 1 of thedrawing is not meant to be exact scale, it is to scale in the respectthat it clearly represents that the distance between the outermost,upwardly-depending electrode members 18 and the base plate of upper arcelectrode assembly 11 is much greater than the interelectrode gaps 25.Similarly, the distance from downwardly-depending arc-electrodes 16 tothe lower plate 17 or arc-electrode 12 is much greater than the distanceof interelectrode gaps 25, as also is the distance between theoutwardly-disposed downwardly-depending electrodes 16 and annular flange26 which protects insulator 14 from Sputtering and short-circuiting.

Once the device 10 has become conducting with a plurality of conductionpaths between adjacent oppositelypoled individual electrode members, theprinciples enunciated hereinbefore of the substantial elimination ofmagnetic forces within the interaction space becomes apparent. Theconduction paths in any individual arc-electrode member, as for example,downwardly-depending arc-electrode members 16, are downwardly incylinder 20 and upwardly in central post 21. Since these currents aresubstantially equal and in opposite directions, the magnetic fieldexternal of the electrode member due to current conduction paths thereinis substantially zero. Similarly, in upwardly depending electrode member18 current concluction is upwardly in cylindrical member 23 anddownwardly in central post 22. As with electrode member 16, thesubstantially equal and opposite conduction paths and magnitude thereofcauses a substantial cancellation of the external magnetic field due tothe conduction path therein and the entire assembly between theindividual arc-electrodes is substantially field-free. Although sidewallmembers 13 surrounds the entire interaction space, there is noconduction of electric current therein and no effect upon the magneticfield, either favorable or unfavorable results from the presence ofmember 13.

In the substantial absence of magnetic field in the interaction spacebetween the arc-electrode members 16 and 18, there is substantially nobody force tending to bunch the numerous conduction paths between theindividual electrode members and thereby anode spots are avoided andvery high currents may be carried before what minimal field remains isetfective to cause any bunching. Accordingly, a very great currentconduction may be obtained with no destructive arcing or erosion of thearc electrodes. In the event that destructive arcing does occur,however, it may occur between only a particular pair of electrodes. Inaccord with the invention, it is a simple matter to cause each ofarc-electrode members 16 and 18 to be individually removable as forexample, with a screw-thread from base members 15 and 17 to make itpossible to dissemble device 10 at seal 14, remove any damaged or erodedarc-electrode member and re-assemble the device, evacuate and re-seal.In devices in accord with the present invention it is possible toconduct currents of the order of hundreds of thousands of amperes atvoltages of 50,000 to 100,000 volts in devices having a volume ofapproximately one cubic foot with substantially no arcing or erosion ofthe electrode members.

FIGURE 2 of the drawing illustrates a vacuum switch constructed inaccord with the present invention. In FIG- URE 2, like members to thoseof FIGURE 1 are identified with the same reference numerals. Vacuumswitch 40 of FIGURE 2 comprises a first upper electrode assembly 11 anda second lower electrode assembly 12 having a plurality ofdownwardly-depending electrode members 16 and upwardly-dependingelectrode members 18, respectively, as in FIGURE 1. Downwardly-dependingelectrode members 16 are comprised of a central post and a concentriccylindrical member capped with a planar disc 21, as areupwardly-depending electrode members 18. The electrode members areinterleaved with one another in alternating fashion, so as to form aperiodic structure as in the device of FIGURE 1. The envelope enclosingthe interaction space of device 40 comprises upper electrode assembly 11and lower electrode assembly 12 joined with a cylindrical, insulatingdielectric sidewall member which may, for example, be fabricated from ahigh temperature glass such as Pyrex or Vycor or a high dielectricstrength ceramic, as for example high density alumina, or a fosterite.Sidewall member 41 supports an insulator shield 42 which is supported bya flange 43 imbedded in an annular bead 44 which is integral with theinner portion of cylindrical sidewall member 41. Means to provide aquantity of ionized particles to cause breakdown between arc-electrodemembers 16 and 18 are provided in the form of a starter electrode 45mounted upon an actuating rod 46, which is reciprocably movable and incontact with disc 21 of individual downwardly-depending electrode member16 by means of a Sylphon bellows 48 which is suitably fastened to theouter periphery of an aperture 49 in lower base plate 17 and similarlyfastened in hermetic seal by plate 48 to actuating rod 46. Starterelectrode 45 is conveniently constructed of a refractory, lowvapor-pressure material, as for example, tungsten or molybdenum. Toinitiate an arc, a force is applied to actuating arm 46, withdrawingstarter electrode 45 from plate 21, causing an initial arc to be struck.Electrode 45 is completely withdrawn and seated within orifice 49 inplate 17. As the electrode 45 is withdrawn from plate 21, the arc ispreferentially caused to spread out into the spaces betweenoppositely-poled electrodes and almost instantaneously the arc spreadsout between the individual electrode members 16 and 18. Although onestarter electrode is shown, any number may be used.

It will be noted from FIGURE 2 that device 40 utilizes a non-conductingsidewall member 41 with an associated shield member 42 and that thedevice of FIGURE 1 utilizes a metallic sidewall member 13. Since thesidewall members bear no significance to the electrical characteristicsof the device, the device of FIGURE 1 may be constructed with theinsulating sidewall member of the device of FIGURE 2. Similarly, thedevice of FIG- URE 2 may be constructed with the metallic sidewallmember of the device of FIGURE 1. Actual structural details depend uponthe intended use and the environment of the device.

FIGURE 3 of the drawing illustrates a plan sectional View of the deviceof FIGURE 1 taken along section lines 3-3. In FIGURE 3, the periodicstructure of upwardly depending electrode members 18 anddownwardlydepending electrode members 16 may readily be seen. It is tobe noted that the interelectrode distance 25 represented by arrows A,which are the conduction paths between adjacent, oppositely-poledindividual electrode members, are the shortest distances between anyopposite polarity member of the device. Similarly, the distance betweenupwardly-depending electrode members 18 and metallic sidewall member 13,which is at the same electrical potential as downwardly-dependingelectrode members 16, is much greater than the interelectrode spacing25. It may further be seen from the illustration of FIG- URE 3 that eachindividual electrode member (other than those of the periphery of theperiodic array) is surrounded by four symmetrically-located,oppositely-poled electrode members. Since the azimuthal magnetic fieldaround any individual electrode member which would be orthogonal toconduction paths between adjacent electrode members is substantiallyzero due to current conduction therein and the folded-back structurethereof, the orthogonal magnetic field within the interaction spacewithin the device is substantially zero, and substantially zero net bodyforce is eifective upon any given conduction path to cause a bunchingthereof and formation of destructive, erosive anode spots.

FIGURE 4 illustrates an alternative structure for a triggerable vacuumgap device constructed in accord with the present invention. In FIGURE4, the gap device includes a first upper arc-electrode member 11 and asecond lower arc-electrode assembly 12 joined in hermetic seal withinsulating dielectric sidewall member 41, as in FIGURE 2. Sidewallmember 41 is protected from the deposition of sputtered or evaporatedmetallic particles and short-circuiting thereof by a shield member 42which is imbedded by a flange 43 in an annular bead 44 on the innersurface of sidewall member 41. Upper electrode assembly 11 includes abase or end wall plate 15 and a plurality of downwardly-dependingelectrode members 50, which are solid, but which may be hollow providedit has sufiicient thermal conductivity, and are terminated at end 51.Lower arc-electrode assembly 12 includes a flat base plate 17 and aplurality of upwardly-depending solid electrode members 52 terminated atends 53. The downwardly-depending electrode members 50 and theupperwardlydepending electrode members 52 of upper and lower electrodeassemblies 11 and 12, respectively, are interleaved between one anotehrto form a periodic structure as in the devices of FIGURES 1 and 2. Meansfor producing an ionized electron-ion plasma to cause the device ofFIGURE 4 to be rendered conductive is provided in the form of a triggerelectrode assembly 25, similar to that of FIGURE 1 of the drawing. Meansfor connecting the device in circuit with an electric load to beswitched, protected, or otherwise controlled, is provided by means ofterminal lugs 30 and 31.

FIGURE of the drawing illustrates, in horizontal plan view, a sectiontaken through lines 5-5 of FIG- URE 4. This plan view of the device ofFIGURE 4 illustrates square or rectangular symmetry, rather thancircular symmetry as is illustrated in the device of FIGURE 3. It shouldbe appreciated, however, that the square or rectangular symmetry ofFIGURE 5 may be utilized with the devices of FIGURES 1 and 2 and thecircular symmetry of FIGURE 3 may be utilized with the device of FIGURE4. In FIGURE 5, it may be readily seen that the periodic structureillustrated in FIGURE 3 is maintained herein, with each ofupwardly-depending electrodes 52 being surrounded by a plurality ofdownwardly-depending electrodes 50 (except at the periphery of thearray). Similarly, it may be seen that the inter-electrode spacings 25are smaller than any spacings between any individual electrode memberand any other member having the same potential as the oppositely-poledelectrode members. It

may also be noted that the individual electrode members are solid,rather than composed of a concentric structure as in the devices ofFIGURES l and 2 illustrated in plan view in FIGURE 3.

FIGURE 6 illustrates a schematic illustration of the field configurationsurrounding an assembly of four juxtaposed electrodes 50 and 52 as inFIGURE 5 of the drawing. This view is taken with all four electrodes insection. In FIGURE 6, interelectrode gaps 25 exist betweenoppositely-poled electrodes 50 and 52. Similarly, since there is nore-entrant structure in the device of FIGURE 4 to cause a folding-backof current conduction path and a net zero magnetic field exterior ofeach electrode, it is apparent that there will be some magnetic field.It has been found, however, that the periodic array of these electrodestructures does not depart markedly from the ideal array in the idealfield configuration obtained in the devices of FIGURES l and 2. InFIGURE 6, the annular area 60, immediately surrounding each ofelectrodes 52 represents a moderately dense azimuthal magnetic field inthe direction indicated by the arrows therein (assuming current into thepaper). Similarly, the annular section 61, immediately surroundingelectrodes 50 represent a moderate azimuthal magnetic field in thedirection of the arrows as shown. Because of the opposite direction ofthe magnetic fields in the interelectrode gaps the majority of the space62 existing outside of annular regions 60 and 61'is substantiallymagnetic field-free and the center portion of the array 63 is exactlymagnetic field-free. Although this field configuration has some effectupon the conduction paths between electrode members 50 and 52, it is notas drastic as one may think and the principles of the present inventionmay still be substantially realized in such a structure. This will beevident from a consideration of FIGURE 7.

In FIGURE 7 a schematic representation of current conduction pathsbetween an upper electrode assembly 11 and a lower electrode assembly 12having only one individual downwardly-depending electrode member 50 andone upwardly-depending electrode member 52 is shown. Current pathswithin arc-electrode members 50 and 52 are represented by arrows C. Ifelectrode members 50 and 52 were of the reentrant type as illustrated inFIGURES 1 and 2 of the drawing, the conduction paths between electrodemembers 50 and 52 would be the sheath enclosed within arrows D. It isapparent, in view of the great area encompassed by the sheath overelectrodes 50 and 52 that the principles of the present invention arerealized almost ideally in that conduction paths are greatly spread outover the electrode surfaces with essentially no bunching. With thestructure as illustrated in FIGURE 4 and FIG- URE 5 of the drawing, themoderate azimuthal magnetic fields 60 and 61, immediately surroundingthe individual electrode members 52 and 50, respectively, tend to exerta moderate body force upon the conduction paths in the immediatevicinity of the electrodes. Since, however, these body forces actingupon the current paths are opposite in direction, the conduction pathsare urged in opposite directions in the immediate vicinity of electrodes50 and 52, causing the current paths to occupy the shaded arearepresented at E in FIGURE 7. Although there is some degree of bunchingof the conduction paths in the solid configuration illustrated in thedevice of FIGURE 4 and further illustrated in FIGURES 6 and 7, it shouldbe readily apparent that the bunching is not sufiiciently great as tocause such an increase in current density sulficient to cause theformation of destructive anode spots at all except relatively highcurrents. While it is conceded that the current carrying capacity ofdevices constructed in accord with the embodiment of FIGURE 4 of thedrawing does exhibit a slightly lower threshold for formation of anodespots, this threshold is nevertheless substantially higher than thatfound in conventional are devices and, to a large measure, theadvantages of the present invention are achieved with a great simplicityof construction utilizing the construction illustrated in FIG- URE 4.

FIGURE 8 of the drawing illustrates still another alternative embodimentof the present invention. In FIG- URE 8, a triggerable vacuum gap device70 includes an upper electrode assembly 11 and a lower electrodeassembly 12, connected in hermetic seal with a cylindrical insulatingsidewall member 41. Upper electrode assembly 11 includes a base plate ordisc 15 and a plurality of downwardly-depending individual electrodemembers 16, each of which is a thin planar vane and which are arrangedradially about the longitudinal axis of device 70. Lower electrodeassembly 12 comprises a base plate or disc 17 and a plurality ofupwardly-depending individual electrode members 18, each of which likethe electrode members 16, is a substantially thin planar vane, and whichare radially disposed about the longitudinal axis of device 70.

Upon assembly of the device, the vanes 16 and the vanes 18 areinterleaved between one another so as to form a periodic structure withalternate vanes connected to one electrode assembly and other alternatevanes connected to the opposite electrode assembly. Assembly is made sothat the interelectrode distance between any given pair ofoppositely-poled electrode members 16 and 18 is equal to the samedistance between any other pair of oppositely-poled electrode members 16and 18 within device 70. A vapor shield 42, supported from a flange 43inbedded in annular bead 44 on the inner surface of cylindrical sidewallmember 13 protects the inner surface thereof from becoming covered withmetal lic particles and short-circuiting. Contact to the electrodeassemblies is made through terminal lugs 30 and 31, respectively. As inthe embodiment of FIGURE 4, the individual vanes which constitute theelectrode members are shorter than the length of the device so that theclosest distance between any portion of the oppositelypoled electrodeassemblies or any other material at the same potential is theinterelectrode gap existing between adjacent electrode members.Conduction between electrode assemblies 11 and 12 is initiated bytrigger electrode assembly 27, which has the identical or functionallysimilar structure to that of the trigger electrode assemblies of thedevices of FIGURES l and 4. In operation, the device 70 is renderedconductive by an electrical pulse to trigger lead 32, to cause theinjection of an electron-ion plasma into the space between individualelectrode members 16 and 18 to cause electrical breakdown therebetween.

FIGURE 9 illustrates, in horizontal section along the lines 9-9 inFIGURE 8, a cross-sectional view of the triggerable vacuum gap 70illustrated in FIGURE 8. As may be seen from FIGURE 9,downwardly-depending electrode members 16 and upwardly-dependingelectrode members 18 are alternately interleaved in an annular patternand define a plurality of interelectrode gaps 25. Trigger assembly 27 isvisible at the center of base plate 17. Since the electrode members ofthe device of FIGURE 8 are not folded-back to cause the elimination ofall magnetic fields, between electrode members 16 and 18, the principlesupon which the present device operates is somewhat modified from that ofthe device of FIGURES 1 and 2, and resembles more nearly the operationof the device of FIGURE 4, although there is a substantial difference.As with the device of FIGURE 4, there is a small region of magneticfield in the region immediately surrounding each of the arc-electrodes16 and 18, electrical conduction within each of the electrode vanesbeing in the same direction. Since, however, the arcing path illustratedas arrow A in FIGURE 9 is acted upon by magnetic forces that are inopposite directions in the immediate vicinity of the respectivearc-electrode members 16 and 18, the distribution of the current pathsbetween, any individual arc-electrode pair is rather similar to thatillustrated at E in FIGURE 7. The field configuration which obtains inthe device of FIGURE 4 and which is 10 illustrated schematically inFIGURE 6 of the drawing does not exist, however, because there is notsuch a periodic structure in which each electrode is surrounded on allfour sides by an electrode member of the opposite polarity.

In all other embodiments of the present invention the force acting uponthe current path between adjacent electrode members has been minimized(except at the region immediately surrounding the electrode members inthe embodiment of FIGURE 4) by causing the magnetic field that isorthogonal to the current to be minimized or eliminated. Thus theproduct approaches zero. In the present embodiment of the invention,essentially the same result will be obtained by allowing B to exist, butby rendering B substantially parallel to J. Thus, for example, since I Bis the vector product if the two vectors are parallel or substantiallyparallel, or even antiparallel, the product equals or approaches zero.In the device of FIGURE 8, such is the case. Turning for the moment toFIGURE 9, it may readily be seen that any two adjacent electrode membersare surrounded by a substantially equal magnetic field due to currentflow in the same direction in the adjacent electrode vanes. Since,however, with respect to the current represented by arrow A, the radialcomponents of the magnetic fields due to current conduction inrespective electrode members substantially cancel in the interveningspace betwen the electrodes and the azimuthal component of the magneticfields due to current conduction in adjacent electrode vanes isadditive. As a result of this characteristic of the magnetic field inthis configuration of the present embodiment, the resultant magneticfield (except in the immediate vicinity of each electrode vane) is anazimuthal field which is substantially parallel with current conductionpaths between adjacent arc-electrodes. Accordingly, due to thisconfiguration the product approaches zero and substantially no bodyforce (other than that which causes the so-called rail-gun configurationillustrated at E in FIGURE 7) is operative upon current conduction pathsbetween the arc-electrode members. As a result current conduction pathbunching at the anode is avoided and destructive anode spots do notform. Accordingly, the configuration illustrated in FIG- URE 9 andincorporated in the device of FIGURE 8 is operative, with a relativelysimple construction, to achieve substantially the same result as themore complicated structures of FIGURES 1 and 2, and to permit thecarrying of exceedingly large values of current within the device 70,without causing a high current density to exist at any place within thedevice to cause the formation of destructive anode spots. Thus, thecurrent threshold for the formation of anode spots is greatly increasedand the current carrying capacity of the device is exceedingly high ascompared with prior art devices.

The foregoing is particularly advantageous, since the construction ofthe device of FIGURE 8, like that of the device of FIGURE 4, isrelatively simple and needs no complicated arrangement requiring closetolerances. Similar to the device of FIGURE 4, the individual electrodevanes may be made removable so that the device may be dissembled bybreaking the seal in the vicinity of upper or lower base plate,replacing one or more arcelectrode members and re-assembling the devicewith a new seal and placing the device back in service for a very smallfraction of the cost it would take to fabricate an entirely new device.

A limiting factor to the effectiveness of the configuration of thedevice of FIGURE 8, illustrated in plan view in FIGURE 9, is the lack ofparallelism between the adjacent arc-electrode members 16 and 18. Thismay readily be remedied by rendering each arc-electrode member 16 and 18wedged-shaped, either in a solid wedge as illustrated in plan view inFIGURE 10, or in a bent V-type wedge as illustrated in plan view inFIGURE 11. Other than the dimunition of the number of vanes utilized inthe attainment of the preferred parallel symmetry of the interelectrodespaces 25, devices constructed with the plan view illustrated in FIGURESand 11 are substantially the equivalent of that illustrated in plan viewin FIG. 9, although improved operating characteristics and highercurrent thresholds for the formation of anode spots are obtained.

From the foregoing, it should be evident that I have provided a newapproach to the concept of raising the threshold for the formationofanode spots in vacuum are devices such as triggera'ble vacuum gaps andvacuum switches by utilizing a periodic structure for the individualarc-electrode assemblies within which a plurality of individualarc-electrode members are interposed interdigitally or interleavedbetween the similar electrode members of the opposite arc-electrodeassembly to cause the creation of a periodic structure which defines aplurality of interelectrode gaps. In these gaps the magnetic fieldorthogonal to the path of current flow between the broad areas of theindividual arc-electrode members is substantially eliminated orminimized, to prevent any body force being operative to cause bunchingof current conduction paths and the formation of destructive anodespots.

Although the invention has been disclosed with respect to specificembodiments, numerous modifications and changes may be made. Thus, forexample, it is within the scope of the present invention that theindividual electrode members, although illustrated with certaincrosssectional areas, mainly circular, may be square, triangular,polygonal, or ay other configuration which provides a broad area ofsubstantially parallel interelectrode spacings to increase the number ofconduction paths between opposite electrodes and minimize the currentdensity. Similarly, circular symmetry may be replaced with a pluralityof elongated parallel electrode members which alternate and which may befolded or vanes, as desired. Many other modifications and changes willoccur to those skilled in the art. Accordingly, I intend, by theappended claims, to cover all such modifications and changes as fallwithin the true spirit and scope of the present invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A vacuum arc discharge device adapted to carry high currents withoutthe formation of anode spots comprising:

(a) an hermetically sealed envelope evacuated to a pressure of 10- tortor less;

(b) a first primary arc-electrode assembly disposed Within said envelopeand including a first plurality of spaced substantially parallelcylindrical electrode members extending substantially normal to a firstendwall member;

(0) a second primary arc-electrode assembly within said envelope andincluding a second plurality of spaced substantially parallelcylindrical electrode members extending substantially normal to a secondendwall member and interleaved in alternating parallel spacedrelationship between the spaced electrode members of said firstarc-electrode assembly;

(d) said first and second spaced cylindrical electrode members providingduring operation a vector prodnot a J X which is insignificantly smallin the spacings between electrode members of first and second electrodeassemblies where J =current density in the arc discharges between anygiven pair of opposite electrode members and B=magnetic field betweenany given pair of electrode members due to current paths within saidelectrode members when said device is in a current conduction condition;

(e) means for causing an electric arc break-down to be establishedbetween said primary arc-electrode assemblies; and

(f) means for connecting said arc-electrode assemblies in circuit withan electric load.

2. The device of claim 1 wherein said first electrode assembly includesan upper base member and a plurality of downwardly-depending electrodemembers and said second electrode assembly includes a base member and aplurality of upwardly-depending electrode members.

3. The device of claim 2 wherein each of said upwardly-depending anddownwardly-depending electrode members is comprised of a central postand a concentric cylindrical member which is joined to said central postat the end thereof that is remote from said base member.

4. The device ofclaim 2 wherein each of said electrode members is in theform of a solid member projecting from said base member.

5. The device of claim 2 wherein said periodic array constitutes apattern in which each electrode member of said first electrode assemblyis surrounded by a plurality of symmetrically arrayed electrode membersof said second electrode assembly except at the periphery of saiddevice.

6. The device of claim 2 wherein said device exhibits circular symmetryabout a longitudinal axis.

7. The device of claim 2 wherein said device is a triggerable vacuum gapdevice and the means for supplying an electronion plasma therein is atrigger electrode assembly.

8. The device of claim 2 wherein the device is a vacuum switch and themeans for supplying an electron-ion plasma therein is a starterelectrode adapted to establish a starter arc discharge therein.

References Cited UNITED STATES PATENTS 3,356,893 12/1967 Lafierty 3l5ll13,356,894 12/1967 Lafierty 315-111 JAMES W. LAWRENCE, Primary ExaminerR. F. HOSSFELD, Assistant Examiner US. Cl. X.R.

